This invention relates to electrostatic printing, and in particular, to a novel electrostatic printing device as well as a novel method of utilizing such a device in the production of an electrostatic latent image.
There have been developed various electrophotographic devices in which an electrostatic latent image is formed corresponding to the visual image of an object which has been projected onto a photoconductive plate. The resulting electrostatic latent image is thereafter developed into a visual image by deposition of powder in a pattern conforming to the electrostatic latent image. Such prior art devices are described in U.S. Pat. Nos. 2,221,776, 2,277,013 and 2,297,691 among others. Each of the aforesaid devices provides a means for first producing an electrostatic latent image into a visual reproduction in a subsequent operation.
While electrophotography is best known as a dry process, considerable effort has been expended on liquid development devices and processes for electrostatic latent images. The advantages thought to be obtainable with liquids include higher speed, greater uniformity, higher resolution, greater ease in handling the developer and self fixing. An early electrophotographic use of liquid developers is disclosed in U.S. Pat. No. 2,551,582 in which a solvent mist is presented to the electrostatic latent image where it is attracted selectively to the charged areas. The solvent image formed in this way can then be transferred to dye transfer paper which in turn is run against a web carrying a soluble dye such as used, for example, in spirit duplicating. Perhaps the most common electrophotographic liquid developer is analogous to the usual powder development arrangement having a carrier fluid with a strong triboelectric effect on a particulate material suspended in the fluid. For example, a pigment is suspended in petroleum solvent and then flowed over the electrostatic latent image so that the pigment deposits out in the image areas by virtue of a triboelectric charge picked up through contact with the carrier liquid. This is disclosed, for example in U.S. Pat. No. 3,010,842. A third type of liquid development is electrolytic in nature and development is produced by metallic ions depositing out of the electrolyte in accordance with the image. An example of this is disclosed in U.S. Pat. No. 3,057,787.